(1) Field of the Invention
This invention relates to an internal combustion engine, particularly to an improved exhaust port assembly in the engine.
(2) Description of the Prior Art
In an internal combustion engine, maintaining the temperature of the exhaust gas is useful to reduce carbon monoxide and hydrocarbons in the exhaust gas and to improve turbo-charger efficiency. For that purpose, a port pipe has been used which is covered by a fibrous ceramic impregnated with an organic salt and which is cast by cast aluminum to form a cylinder head block of an engine. But, the port has some disadvantages, for example, (1) softness of the fibrous ceramic layer was lost and the layer tends to be broken by mechanical shaking or thermal shock, (2) the manufacturing process requires a step of drying and sintering the impregnated salt and this results in an expensive added cost, and (3) the fibrous ceramic layer includes a lot of pores even after being impregnated. At casting, molten aluminum goes into the pores so that heat insulation capability tends to be lost.